Jarring device

A jar for providing an impact to a tool string stuck in a wellbore, the jar comprising:

• a housing and a mandrel configured to move relative to the housing, and
• a release mechanism actuatable to fire the jar to cause the housing and mandrel to collide by the action of an applied tension to cause an impact to the tool string, and
• a transducer configured to measure the axial position of the mandrel relative to the housing to allow for a real-time measurement of the jar status at the surface based on the measured axial position, and
• wherein the transducer is a linear variable differential transformer comprising:
• a primary coil and two secondary coils mounted to the housing, and
• a core comprising a magnetic permeability material fixed to the mandrel and received within a bore of the coils to move axially with the mandrel therein, the core comprising a non-magnetic portion fixed to the mandrel and the magnetic permeable material mounted to the non-magnetic portion,
• wherein the mandrel is hollow, and wherein the non-magnetic portion of the core is a hollow cylinder connected in-line with the mandrel, an inside of the mandrel and the core providing a conduit for electrical conductors to pass through the jar.